JPH0746680B2 - Exposure equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exposure apparatus used in a photolithography process among manufacturing processes of semiconductor devices such as IC and LSI.

As a specific example, there is an apparatus for projecting and exposing a pattern on a reticle onto a semiconductor substrate (wafer) by using a projection optical system, and an alignment optical for aligning the pattern on the reticle and the pattern on the semiconductor substrate. The present invention relates to an exposure apparatus in which a system and the entire apparatus including a projection optical system are matched.

[Prior Art] Conventionally, in this type of apparatus for relatively positioning a wafer and a reticle by using a laser in a state of being superposed through a projection lens, a transmission image and a reflection image of the reticle mark and a reflection of the wafer mark are reflected. Image is detected, and one image from the reticle interferes with the other image or the image from the wafer, which adversely affects the detection of the relative positional relationship between the wafer and the reticle. . As an example to prevent it, put a λ / 4 plate in the projection lens,
There is one in which the reticle signal and the wafer signal are separated in the polarization direction and observed.

[Problems to be Solved by the Invention] However, according to such a conventional technique, a signal light processing optical system having two systems of a reticle system (hereinafter referred to as MD system) and a wafer system (hereinafter referred to as MW system) is provided. I had to have two eyes on each side.

Also, in the conventional method, the reticle thickness is a design parameter of the observation optical system, so when the reticle thickness changes, the observation optical system is placed at the appropriate position (the optimum distance between the reticle and the observation optical system). The difference between the reticle thickness and the standard thickness made the specifications of the exposure apparatus custom-ordered.

The present invention does not require separate signal processing systems of the MD system and the MW system in the above-mentioned conventional example, that is, it is not necessary to separate each signal, and therefore, the λ / 4 plate in the projection lens can be removed, It is an object of the present invention to provide an exposure apparatus having a simpler and lower cost alignment system and a projection lens.

[Means and Actions for Solving Problems] In order to achieve this object, the exposure apparatus of the present invention uses a projection lens for projecting and exposing a pattern on a reticle onto a resist-coated wafer, and a non-exposure wavelength light. A light beam separating means for separating a certain light beam into two light beams, one of the separated light beams to illuminate a mark on the reticle, and the other light beam to illuminate a mark on the wafer through the projection lens. Of the reflected light of each of them is returned to the original optical path, combined by the light beam separating means, and observed, and the astigmatism and coma aberration generated when the other light beam passes through the projection lens. An ascoma correction optical system for correction is provided in the optical path of the other light beam.

According to this method, the light flux which is the non-exposure wavelength light is separated into two light fluxes, and each light flux irradiates the marks on the reticle and the wafer, and the reflected lights are combined again for observation. The signal lights from the two are observed without interfering with each other and without being interfered with each other. In particular, an ascoma correction optical system for correcting astigmatism and coma generated when the light flux passes through the projection lens is provided in the optical path of the light flux that detects the mark on the wafer. With the light flux of the exposure wavelength, the reflected image of the mark on the wafer observed via the off-axis of the projection lens is faithfully formed. As a result, without exposing the resist on the wafer, the images of the marks on the reticle and the wafer can be well formed and observed without interfering with each other, and the positional relationship between the reticle and the wafer can be directly observed by one detection system. To be detected. Therefore, highly accurate alignment between the reticle and the wafer can be achieved with a simple and low-cost alignment system.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

1 to 3 show an embodiment of the present invention. Referring to FIG. 1, 1 is a reticle, 2 is a projection lens, 3 is a wafer,
4 is a movable mirror, 5a and 5b are mirrors, 6 is an objective lens, 7
Is an illumination lens, 8 is an optical fiber, 9a and 9b are half prisms, 10 is a relay lens, 11 is an elector, 12 is a spatial filter, and 13 is a CCD camera. Reference numeral 15 shown in FIG. 3 is an ascoma correction optical system. Reference numerals 16 and 17 in FIGS. 2 and 3 denote positions corresponding to the conventional reticle side alignment mark aligned with the alignment mark on the wafer side scribe line, and 17 and 17a are reticle side alignment mark positions in this embodiment. 19 in FIG. 1 is an XY stage.

The optical path and the signal light path of this embodiment will be briefly described with reference to the conceptual diagram of FIG.

Illumination light having the same wavelength as the exposure light using the fiber 8 as a light source in the figure enters the half prism 9b through the illumination lens 7, the half prism 9a, the mirror 5a and the objective lens 6, and is converted into reflected light and transmitted light. Branched. The reflected light enters the movable mirror 4 through the mirror 5b, is bent by the movable mirror 4, and then reaches the lens image plane side (wafer) via the projection lens 2. The light thus reached illuminates the mark on the wafer side, and the resulting wafer-side observation signal light traces the above optical path in the reverse direction, and the movable mirror 4, the mirror 5b, the half prism 9b, the objective lens 6 and the mirror 5a. After passing through the half prism 9a, the light passes through the relay lens 10, the elector 11 and the spatial filter 12, and enters the CCD camera 13.

On the other hand, the illumination light that has passed through the half prism 9b irradiates the pattern surface side of the reticle as it is, and the observation signal light also passes through the half prism 9b, then passes through the objective lens 6 and the mirror 5a, and then through the half prism 9a. Lens 1
CCD camera 13 through 0, erector 11 and spatial filter 12
to go into.

In the image processing device (not shown), the CCD camera 13
The video signal output from the wafer 3 and the reticle 1 are received.
Image processing is performed to check the relative alignment state of.

That is, in the present embodiment, the light beam for wafer observation and the light beam for reticle observation are separated to prevent mutual signal interference.

FIG. 2 is an explanatory view developed around the reticle 1 of this embodiment shown in FIG. In the figure, for convenience of description, the mirror 5b between the movable mirror 4 and the half prism 9b is removed, and it is expanded in the lateral direction. Further, although the movable mirror 4 is shown in the state in which it is thrown into the exposure light flux, the broken line 4b is shown so as not to interrupt the exposure light flux after the completion of the relative alignment.
Retreat to the position.

In the state shown in FIG. 2, the movable mirror 4 put into the exposure light beam.
The optical path formed by the above is referred to as a first branched optical path, and the optical path formed by the half prism 9b arranged on the first branched optical path is referred to as a second branched optical path.

As described above, the illumination light incident through the objective lens 6 is divided into two by the half mirror surface of the half prism 9b. A portion of the one half mirror surface that is bent advances along the first branched optical path and forms an image at the focal position of the objective lens 6 on the optical path. In addition, the movable mirror 4
Of the projection lens 2 from the image plane to the projection lens 2
A part of the light flux that has come to the object plane side (reticle side) is bent by the movable mirror 4 and travels on the first branch optical path to form an image at a position corresponding to the object plane side focal position of the projection lens 2. The marks on the wafer can be illuminated and observed by matching these two imaging points.

Further, the portion of the half prism 9b that has directly transmitted through the half mirror surface travels on the second branch optical path. here,
By aligning the focus of the objective lens 6 on the optical path with the pattern surface side of the reticle 1, the reticle side alignment mark can be illuminated and observed.

That is, in this embodiment, since the half prism 9b has a cube shape, if the distance from the center of the luminous flux of the movable mirror 4 to the pattern surface of the reticle 1 is L ₁ as shown in FIG. From the projection lens 2 bent by the movable mirror 4 to the image forming point of the light beam, the distance from the center of the light beam in the half prism 9b to the focus of the objective lens 6 on the first branch optical path, and in the half prism 9b. Objective lens 6 on the second branch optical path from the center of the luminous flux of
The distance to the focus (i.e., the distance from the half prism 9b to the pattern surface of the reticle 1) are all equal to L _1, also combined the positions to make it so.

[Modification of Example] Although the observation optical system using the exposure wavelength light as the observation light has been described in the above-mentioned embodiments, the present invention uses light having a wavelength different from that of the exposure light as shown in FIG. It can be easily adapted to the existing observation method. In this case, in order to correct astigmatism and coma generated between the movable mirror 4 and the half prism 9b in the first branch optical path due to the relationship between the light of the wavelength used for observation and the projection lens 2. Add optical system 15 of. Further, as shown in the figure, the respective components may be arranged so that axial chromatic aberration ΔL, which is another aberration caused by the relationship between the observation light and the projection lens 2, is absorbed in the first branched optical path. If the observation light is a non-exposure wavelength light as in this modified example, the mark preservation on the wafer side is complete, and it is possible to cope with the condition that the process is involved such as when using a g-ray absorbing resist.

[Effects of the Invention] As described above, according to the present invention, it is possible to observe marks on a reticle and a wafer in a precise positional relationship with a simple structure without interference of signal light or aberration of a projection lens. You can Therefore, highly accurate alignment between the reticle and the wafer can be achieved with a simple and low-cost alignment system.

[Brief description of drawings]

FIG. 1 is a conceptual diagram according to one embodiment of the present invention, FIG. 2 is an explanatory diagram of the embodiment of FIG. 1, and FIG. 3 is a modification of the portion of FIG. 1: reticle, 2: projection lens, 3: wafer, 4: movable mirror,
5a, 5b: Mirror, 6: Objective lens, 7: Illumination lens, 8: Optical fiber, 9a, 9b: Half prism, 10: Relay lens, 11: Electa, 12: Spatial filter, 13: CCD camera, 16: Conventional Reticle-side alignment mark positions 17, 17a: reticle-side alignment mark positions according to the present invention.

Claims (1)

[Claims] 1. A projection lens for projecting and exposing a pattern on a reticle onto a resist-coated wafer, and a light beam separating means for separating a light beam which is a non-exposure wavelength light into two light beams.
The separated light flux illuminates the mark on the reticle, the other light flux illuminates the mark on the wafer through the projection lens, and returns each reflected light to the original optical path to separate the light flux. An ascoma correction optical system for correcting astigmatism and coma generated when the other light flux passes through the projection lens. An exposure apparatus provided in the optical path.